Diabetes is on the rise around the world, and nowhere more rapidly than in developing countries that are adopting the sugary, starchy diet that has plagued the richer world for years. And it turns out that Asians, and especially South Asians, are particularly vulnerable.

The nutritionist runs a white measuring tape around my waist. I defy the urge to suck in my stomach.

I'm 42 years old, a mother of two and a journalist based in India's capital, Delhi, currently one of the world's most polluted cities. I eat organic food, rarely snack, and consider myself pretty slim and active, especially compared to my American friends, whom I can see on Facebook are generally twice my girth.

"It's 87cm (34.25in)," says Chaya Ranasinghe, nutritionist at Sri Lanka's National Diabetes Centre. I'm here to find out why slim-looking Indians and Sri Lankans are increasingly falling victim to type 2 diabetes - a disease we tend to associate with people who anyone could see were obese.

"Not bad," I say. "That's pretty honourable for my age."

"Yes, but it should be 80cm (31.5in) maximum," she replies. "You are 7cm (2.75in) over."

"Should have sucked in my waist," I fume belatedly.

Chaya is helping me assess my risk for diabetes and the waist measurement is key for people of Asian origin. That's because Asian genes dictate that fat is laid down in the abdominal area.

It's this "visceral" or belly fat, as well as fat inside the liver, that puts us at risk.

"Imaging technology that measures fat in humans has shown that Asians of a healthy BMI have more fat around organs and in the belly area than Europeans with the same BMI, thereby increasing risk," according to a 2009 report in the Journal of the American Medical Association.

Fat makes tissue resistant to insulin, the hormone that regulates blood sugar, so the glucose builds up, and can eventually trigger type 2 diabetes.

According to some researchers, Asians, and especially South Asians, are more likely to have not only more abdominal fat, but also less muscle, which further increases insulin resistance.

In addition, Asian women are at greater risk of suffering from diabetes during pregnancy, which can put their children at risk of type 2 diabetes in later life.

That's why the waist measurement - 80cm (31.5in) for Asian women and 90cm (35.5in) for men - is a good indicator of diabetes risk, along with five other factors: family history of the disease, smoking, drinking, exercise and stress levels.

My "lifestyle consultation" reveals that I'm at risk on five of those six factors - all except smoking.

This is getting serious.

"Asians have what we call the "thrifty" phenotype which means our bodies are designed to conserve energy and lay down food in the form of fat," explains Prof Chandrika Wijeyaratne, who runs NIROGI Lanka, a diabetes prevention task force.

"But when we conserve energy in today's environment of unhealthy food, we conserve way, way too much."

Wijeyaratne explains that body mass index (BMI) standards, which help classify people as "normal", "overweight" and "obese", need to be adjusted for Asians.

For the average Westerner, it takes a BMI of 25 to 30 to be considered overweight, she says, but a person of Asian origin need only have a BMI of 23 to 25.

"And it's a misconception that sugar alone causes diabetes," she tells me. "Starch is a big problem too."

When nutritionist Chaya Ranasinghe takes me to a local grocery shop, I point proudly to fresh fruits and vegetables, which I eat regularly.

However, we then come face to face with an unexpected culprit: rice.

This is a food I've always considered the epitome of healthy Asian cuisine. But it turns out that white rice, which is polished and processed, is not what my body - genetically speaking - is adapted to.

"You should be eating red or brown rice," Chaya tells me. "White rice has had the husk - or fibre -removed, so it's faster to digest. It means you eat more, it fills you up less, and turns to sugar more quickly in the blood."

I'm stunned. I eat at least two bowls of rice each day. I've always thought of rice as my birthright, and a healthy one at that.

Globally, the WHO says at least 350 million people live with type 2 diabetes and the number is set to rise to half a billion in two decades' time.

"It's a frightening situation - diabetes is of tsunami proportions, and South Asia is at the epicentre," says Wijeyaratne.

China is recognised as the world's diabetes capital with 109 million diabetics, or nearly 10% of the population.

According to the Diabetes Atlas, compiled by the International Diabetes Federation, India has 69 million diabetics, or 9% of the population. However, there is insufficient screening in India and only the most rudimentary health system, so the numbers may be far higher.

In Sri Lanka, 10% of the population already have diabetes and another 10% show early signs of it - that's a total of four million people on this island nation of sunny beaches, fresh fruit and seafood alone.

According to 10-year-old data from the World Health Organization more than a quarter of Sri Lanka's population is overweight. Only 17% eat the recommended five or more servings of fresh fruit and vegetables daily and a whopping 88% have one-to-three raised risk factors for diabetes.

"Eight to 10 years ago, we were talking about type 2 diabetes in middle age. Now, increasingly, I'm seeing more and more young people, in their 20s, and more worryingly, school children between 12 and 18 years old," says Dr Manilka Sumanatilleke at his diabetes clinic, in Karapitiya Hospital on the country's idyllic south-west coast.

"I see at least one or two such young patients per month in this clinic."

He blames the popularity of white rice, stir-fried in coconut oil, as well as kottu - a fried bread stuffed with meat and vegetables.

"They love it, but it is very unhealthy," he said.

The country's national health system is struggling to cope with the huge rise in patients with chronic illnesses like diabetes. Infectious and other communicable diseases now account for only 10% of the demand on the country's health service. Non-infectious diseases - diabetes, cancer and asthma, for example - swallow up the other 90%.

At the National Hospital in central Colombo, Prof Mandika Wijeyaratne witnesses the human cost of diabetes every day. A surgeon, he amputates the limbs of patients whose untreated diabetes has ravaged blood vessels, leading to loss of feeling and simple, but often catastrophic, injuries.

"It always starts with a tiny wound," he says showing me around Ward 28. "Here is a patient who's had below-knee amputation. This all started with a little injury - he stepped on a sharp stone barefoot. His infection spread upwards very quickly. To save his life, we had to take off half his leg.

"The situation here has got much worse in the last 20 years. Then, it was smokers' problems. Now it's shifted mainly to diabetics."

As I head back to Delhi, I consider my risk factors and plot what changes I can make immediately.

A few months on, I no longer eat white rice. Instead, I've switched to red rice, which I enjoy, even in biryanis and stir-fries.

I must do more exercise, but Delhi is a dense, chaotic urban jungle where pavements are broken, traffic omnipresent, and clean parks few and far between. Not to mention it's become the world's air pollution capital with levels of fine toxic particles twice as high on average as Beijing's.

In truth, most days the only exercise I get is walking the 10 steps from my bedroom to my office, where I sit editing radio interviews or writing on my computer. Even when I do need to get out and about, it's by car, the fastest, safest option.

But I've seen my grandmother die from diabetes complications. And recently my father, who has stubbornly refused to confront his blood sugar levels, was diagnosed with retinopathy, where diabetes damages the fine blood vessels in the eye. Vision loss is irreversible.

I may not escape the same fate unless I accept that my DNA is unforgiving and make drastic changes in my behaviour now.

For me, those changes include a decision to move somewhere less polluted, where physical exercise is easier. For millions of South Asians, arresting the runaway growth of diabetes will have to involve waking up to the problem, and making fundamental changes to the way people eat, work and play.